1. Field of the Invention
A toroidal type continuously variable transmission according to the present invention is utilized as an automatic transmission for an automobile of which the output is relatively great.
2. Related Background Art
It has been studied to use a toroidal type continuously variable transmission as schematically shown in FIGS. 5 and 6 of the accompanying drawings as a transmission for an automobile. This toroidal type continuously variable transmission is such that as disclosed, for example, in Japanese Laid-Open Utility Model Application No. 62-71465, an input side disc 2 is supported concentrically with an input shaft 1 and an output side disc 4 is fixed to the end portion of an output shaft 3 disposed concentrically with the input shaft 1. Inside a casing containing the toroidal type continuously variable transmission therein, there are provided trunnions 6, 6 pivotable about pivots 5, 5 located at positions twisted relative to the input shaft 1 and the output shaft 3.
These trunnions 6, 6 are provided with the pivots 5, 5 on the outer sides of the opposite end portions thereof. Also, the base end portions of displaceable shafts 7, 7 are supported on the central portions of the trunnions 6, 6 and the trunnions 6, 6 are pivotally moved about the pivots 5, 5, whereby the angles of inclination of the displaceable shafts 7, 7 are made adjustable. Power rollers 8, 8 are rotatably supported around the displaceable shafts 7, 7 supported on the trunnions 6, 6. These power rollers 8, 8 are sandwiched between the input side disc 2 and the output side disc 4. The inner sides 2a and 4a of the input side and output side discs 2 and 4, respectively, which are opposed to each other have their cross-sections forming a concave surface provided by an arc about the pivot 5 being rotated. The peripheral surfaces 8a, 8a of the power rollers which are formed into spherical convex surfaces are made to bear the aforementioned inner sides 2a and 4a.
A pressing device 9 of the loading cam type is provided between the input shaft 1 and the input side disc 2, and the input side disc 2 is resiliently pressed toward the output side disc 4 by the pressing device 9. This pressing device 9 is comprised of a cam plate 10 rotatable with the input shaft 1, and a plurality of (e.g. four) rollers 12, 12 retained by a retainer 11. A cam surface 13 which is an uneven surface extending in the circumferential direction is formed on one side (the right side as viewed in FIGS. 5 and 6) of the cam plate 10, and a similar cam surface 14 is formed on the outer side (the left side as viewed in FIGS. 5 and 6) of the input side disc 2. The plurality of rollers 12, 12 are supported for rotation about shafts radial relative to the center of the input shaft 1.
When during the use of the toroidal type continuously variable transmission constructed as described above, the cam plate 10 rotates with the rotation of the input shaft 1, the plurality of rollers 12, 12 are pressed against the cam surface 14 which is the outer side of the input side disc 2 by the cam surface 13. As the result, the input side disc 2 is pressed by the plurality of power rollers 8, 8 and at the same time, the input side disc 2 is rotated on the basis of the pressing of the pair of cam surfaces 13, 14 and the plurality of rollers 12, 12 against each other. This rotation of the input side disc 2 is transmitted to the output side disc 4 through the plurality of power rollers 8, 8, whereby the output shaft 3 fixed to this output side disc 4 is rotated.
When the rotational speed ratio (transmission gear ratio) between the input shaft 1 and the output shaft 3 is to be changed, when deceleration is first to be effected between the input shaft 1 and the output shaft 3, the trunnions 6, 6 are pivotally moved about the pivots 5, 5 and the displaceable shafts 7, 7 are inclined so that the peripheral surfaces 8a, 8a of the power rollers 8, 8 may bear against the nearly central portion of the inner side 2a of the input side disc 2 and the nearly outer peripheral portion of the inner side 4a of the output side disc 4, respectively, as shown in FIG. 5. When conversely, acceleration is to be effected, the trunnions 6, 6 are pivotally moved about the pivots 5, 5 and the displaceable shafts 7, 7 are inclined so that the peripheral surfaces 8a, 8a of the power rollers 8, 8 may bear against the nearly outer peripheral portion of the inner side 2a of the input side disc 2 and the nearly central portion of the inner side 4a of the output side disc 4, respectively, as shown in FIG. 6. If the angle of inclination of each of the displaceable shafts 7, 7 is made medium between FIGS. 5 and 6, a medium transmission gear ratio will be obtained between the input shaft 1 and the output shaft 3.
FIGS. 7 and 8 of the accompanying drawings show a toroidal type continuously variable transmission described in Japanese Utility Model Application No. 63-69293 (Japanese Laid-Open Utility Model Application No. 1-17352) which has been made more specific. An input side disc 2 and an output side disc 4 are rotatably supported around a tubular input shaft 15 through needle bearings 16, 16, respectively. A cam plate 10 is spline-engaged with the outer peripheral surface of the end portion (the left end portion as viewed in FIG. 7) of the input shaft 15, and is prevented from moving away from the input side disc 2 by a flange portion 17. This cam plate 10 and rollers 12, 12 together constitute a pressing device 9 of the loading cam type for rotating the input side disc 2 while pressing it toward the output side disc 4. An output gear 18 is coupled to the output side disc 4 by keys 19, 19 so that the output side disc 4 and the output gear 18 may be rotated in synchronism with each other.
The opposite end portions of the pair of trunnions 6, 6 are supported on a pair of plates 20, 20 for pivotal movement and displacement in the axial direction (the front to back direction as viewed in FIG. 7, or the left to right direction as viewed in FIG. 8). Displaceable shafts 7, 7 are supported in circular holes 23, 23 formed in the intermediate portions of the trunnions 6, 6. The displaceable shafts 7, 7 have support shaft portions 21, 21 parallel to each other and eccentric with respect to each other and pivot portions 22, 22. The support shaft portions 21, 21 are rotatably supported inside the circular holes 23, 23 through needle bearings 24, 24. Also, power rollers 8, 8 are rotatably supported around the pivot portions 22, 22 through radial needle bearings 25, 25.
The pair of displaceable shafts 7, 7 are provided at opposite positions of 180.degree. with respect to the input shaft 15. Also, the direction in which the pivot portions 22, 22 of the displaceable shafts 7, 7 are eccentric relative to the support shaft portions 21, 21 is the same direction (a direction opposite to the left to right direction as viewed in FIG. 8) with respect to the direction of rotation of the input side and output side discs 2 and 4. Also, the direction of eccentricity is a direction substantially orthogonal to the direction of disposition of the input shaft 15. Accordingly, the power rollers 8, 8 are supported for some displacement in the direction of disposition of the input shaft 15. As the result, even when due to the dimensional accuracy of each constituent, the resilient deformation of each constituent during the transmission of power, etc., the power rollers 8, 8 tend to be displaced in the axial direction of the input shaft 15 (the left to right direction as viewed in FIG. 7 or the front to back direction as viewed in FIG. 8), this placement can be absorbed without any unreasonable force being applied to each constituent.
Also, between the outer sides of the power rollers 8, 8 and the inner sides of the intermediate portion of the trunnions 6, 6, thrust ball bearings 26, 26 for supporting the power rollers 8, 8, and thrust needle bearings 27, 27 for supporting thrust loads applied to outer races 28, 28 which will be described next are provided in succession from the outer sides of the power rollers 8, 8. The thrust ball bearings 26, 26 permit the rotation of the power rollers 8, 8 while supporting the loads in the thrust direction applied to the power rollers 8, 8. Also, the thrust needle bearings 27, 27 permit the outer races 28, 28 and the pivot portions 22, 22 to pivotally move about the support shaft portions 21, 21 while supporting thrust loads applied to the outer races 28, 28 constituting the thrust ball bearings 26, 26.
Further, driving rods 29, 29 are coupled to one end portion (the left end portion as viewed in FIG. 8) of the trunnions 6, 6 and driving pistons 30, 30 are secured to the outer peripheral surfaces of the intermediate portions of the driving rods 29, 29. These driving pistons 30, 30 are oil-tightly fitted in driving cylinders 31, 31, respectively. These driving pistons 30, 30 and driving cylinders 31, 31 together constitute an actuator for displacing the trunnions 6, 6 axially of the pivots 5, 5.
During the operation of the toroidal type continuously variable transmission constructed as described above, the rotation of the input shaft 15 is transmitted to the input side disc 2 through the pressing device 9. The rotation of this input side disc 2 is transmitted to the output side disc 4 through the pair of power rollers 8, 8 and further the rotation of this output side disc 4 is taken out from the output gear 18.
When the rotational speed ratio between the input shaft 15 and the output gear 18 is to be changed, the pair of driving pistons 30, 30 are displaced by the same distance in opposite directions. With the displacement of these driving pistons 30, 30, the pair of trunnions 6, 6 are displaced in opposite directions and for example, the lower power roller 8 as viewed in FIG. 8 is displaced to the right side and the upper power roller 8 as viewed in FIG. 8 is displaced to the left side. As the result, the direction of a force in the tangential direction acting on the portions of contact between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner sides 2a and 4a of the input side disc.2 and the output side disc 4, respectively, changes. With this change in the direction of this force, the trunnions 6, 6 pivotally move in opposite directions about the pivots 5, 5 pivotally supported on the support plates 20, 20. As the result, as shown in FIGS. 5 and 6, the positions of contact between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the aforementioned inner sides 2a, 4a change, and the rotational speed ratio between the input shaft 15 and the output gear 18 changes.
Also, arcuate surfaces 32, 32 concentric with the pivots 5, 5 are formed on the outer peripheral surfaces of the end portions of the trunnions 6, 6. A cable 33 as shown in FIG. 9 of the accompanying drawings is extended in an X-shape between these two arcuate surfaces 32, 32. Fastenings 34, 34 are provided on those portions of this cable 33 which correspond to the arcuate surfaces 32, 32, and these fastenings are engaged with concave stepped portions formed in the intermediate portions of the arcuate surfaces 32, 32 to thereby prevent the cable 33 and the arcuate surfaces 32, 32 from slipping. Such a cable 33 has the role of synchronizing the tilting movements (pivotal movements about the pivots 5, 5) of the two trunnions with each other. Even during the trouble of an actuator (hydraulic driving apparatus) comprised of the driving rods 29, 29, the driving pistons 30, 30, the driving cylinders 31, 31, etc., the cable 33 tilts the trunnions 6, 6 in synchronism with each-other. Accordingly, it never happens that even during the trouble of the actuator, the direction of inclination of the plurality of power rollers 8, 8 sandwiched between the input side disc 2 and the output side disc 4 forming a pair becomes irregular. As the result, it never happens that an excessively great frictional force acts between the inner sides 2a, 4a of the discs 2, 4 and the peripheral surfaces 8a, 8a of the power rollers 8, 8 and thus, it never happens that the toroidal type continuously variable transmission is subjected to fatal damage, and moreover minimum power transmission can be secured.
In both of the toroidal type continuously variable transmissions shown in FIGS. 5 and 6 and FIGS. 7 and 8, two power rollers 8, 8 are provided in the cavity between the inner side 2a of the input side disc 2 and the inner side 4a of the output side disc 4 which are opposed to each other. The two power rollers 8, 8 are disposed on diametrally opposite sides with respect to the centers of rotation of the two discs 2 and 4. In contrast, a toroidal type continuously variable transmission in which three power rollers are provided in the cavity between the inner side of an input side disc and the inner side of an output side disc which are opposed to each other, whereby great power can be transmitted between the two discs is also known as described, for example, in Japanese Laid-Open Patent Application No. 3-74667.
FIG. 10 of the accompanying drawings shows such prior-art structure. The intermediate portions of supporting pieces 36, 36 each bent to 120.degree. are pivotally supported at three circumferentially equidistant positions on a fixed frame 35. Trunnions 6, 6 are supported between the adjacent supporting pieces 36, 36 for pivotal movement and displacement in the axial direction thereof. One end of each of driving rods 29, 29 is connected to one end portion of each of these trunnions 6, 6, and the other ends of the driving rods 29, 29 are connected to the driving pistons 30, 30 of driving cylinders 31, 31 which are an actuator. The driving cylinders 31, 31 lead to the discharge port of a pump 38 which is an oil pressure source through a control valve 37. This control valve 37 is provided with a sleeve 39 and a spool which are displaceable in the axial direction (the left to right direction as viewed in FIG. 10).
When the angles of inclination of the power rollers 8, 8 pivotally supported on the trunnions 6, 6 by displaceable shafts 7, 7 are to be changed, the sleeve 39 is axially displaced by a control motor 41. As the result, pressure oil discharged from the pump 38 is fed into the driving cylinders 31, 31 through hydraulic piping. By this pressure oil, the driving pistons 30, 30 fitted in the driving cylinders 31, 31 are displaced in the same direction with respect to the direction of rotation of the input side disc 2 and the output side disc 4 (see FIGS. 5 to 7). The operating oil forced out of the driving cylinders 31, 31 with the displacement of the driving pistons 30, 30 is returned to an oil reservoir 42 through hydraulic piping (partly not shown) also including the control valve 37.
On the other hand, the displacement of the driving piston 30 resulting from the feeding-in of the pressure oil is transmitted to the spool 40 through a cam 43 and a link 44 to thereby displace this spool 40 in the axial direction. As the result, in a state in which the driving piston 30 has been displaced by a predetermined amount, the flow path of the control valve 37 is closed and the supply and discharge of the pressure oil to the driving cylinders 31, 31 are stopped. Accordingly, the amounts of displacement of the trunnions in the axial direction and further, the angles of inclination of the power rollers 8, 8 become ones only corresponding to the amount of displacement of the sleeve 39 by the control motor 41. The basic structure for changing the angles of inclination of the power rollers 8, 8 by a predetermined amount may be the structure as shown in FIG. 10 wherein three power rollers are provided in the cavity or the structure as shown in FIGS. 5 to 8 wherein two power rollers are provided in the cavity.
Also, when a toroidal type continuously variable transmission is utilized as a transmission for an automobile having an engine of a greater output, it is known as described, for example, in Japanese Laid-Open Patent Application No. 4-69439, etc. to provide each two input side discs 2 and output side discs 4 to secure transmittable power, and arrange these each two input side discs 2 and output side discs 4 in parallel to the direction of transmission of the power. FIG. 11 of the accompanying drawings shows the structure described in this publication.
In this prior-art structure, an input shaft 15 is supported inside a housing 45 for rotation only. This input shaft 15 comprises a first half portion 15a coupled to a driving shaft for feeding power into the toroidal type continuously variable transmission, and a second half portion 15b somewhat rotatable relative to the first half portion 15a. Near the opposite end portions of the second half portion 15b corresponding to a rotary shaft in the axial direction (the left to right direction as viewed in FIG. 11) thereof, a pair of input side discs 2, 2 corresponding to first and second discs are supported through ball splines 46, 46 with their respective inner sides 2a, 2a corresponding to first concave surfaces opposed to each other.
A washer plate 47 and belleville springs 48, 48 are provided in series with each other between the back (a surface axially opposite to the inner side 2a) of one (right as viewed in FIG. 11) input side disc 2 and a loading nut 87 secured to the end portion of the first half portion 15a. Also, a thrust needle bearing 49 and belleville springs 48, 48 are provided in series with each other between the back of the other (left as viewed in FIG. 11) input side disc 2 and the portion near the inner periphery of one surface (the right side as viewed in FIG. 11) of a cam plate 10 constituting a pressing device 9. This thrust needle bearing 49 compensates for the relative rotation of the cam plate 10 and the other input side disc 2. Also, pre-loads toward the output side discs 4, 4 which will be described next are imparted to the input side discs 2, 2 by the belleville springs 48, 48.
Around the intermediate portion of the second half portion 15b, the pair of output side discs 4, 4 corresponding to third and fourth discs are supported for rotation relative to the image shaft 15 with their respective inner sides 4a, 4a corresponding to second concave surfaces opposed to the inner sides 2a, 2a of the input side discs 2, 2. Also, a plurality of power rollers 8, 8 rotatably supported on a plurality of trunnions 6, 6 through a displaceable shaft 7 (see FIGS. 5 to 8) are sandwiched between the inner sides 2a, 4a of the input side and output side discs 2 and 4. The power rollers 8, 8 are inclined in synchronism with each other to make the transmission gear ratios between the input side discs 2, 2 and the output side discs 4, 4 coincident with each other.
Also, on a portion inside the housing 45 and opposite to the first half portion 15a, an output shaft 50 is rotatably supported concentrically with and bearings 55, 55 are provided between the inner peripheral surface of portions of the output side discs 4, 4 which protrude from the sleeve 53 and the outer peripheral surface of the input shaft 15. These roller bearings 55, 55 permit the relative rotation and axial relative displacement of the output side discs 4, 4 and the input shaft 15.
On the other hand, inside the housing 45, a transmission shaft 56 is rotatably supported in parallelism to the input shaft 15 and the output shaft 50. A first transmission gear 57 fixed to one end (the left end as viewed in FIG. 11) of the transmission shaft 50 and the output gear 18a are brought into direct meshing engagement with each other, and a second transmission gear 58 fixed to the other end (the right end as viewed in FIG. 11) independently of the second half portion 15b of the input shaft 15. Rotation transmitting means is provided between the output shaft 50 and the pair of output side discs 4, 4, whereby the rotation of the output side discs 4, 4 is transmittable to the output shaft 50.
In the inside portion of a through-hole 52 formed in a partition wall 51 present in a portion inside the housing 45 and between the pair of output side discs 4, 4, a tubular sleeve 53 is supported by a pair of anti-friction bearings 54, 54 to constitute the rotation transmitting means. The pair of output side discs 4, 4 are spline-engaged with the opposite end portions of this sleeve 53. An output gear 18a is secured to the intermediate portion of the sleeve 53 and the inside portion of the partition wall 51. Further, roller of the transmission shaft 56 and a third transmission gear 59 fixed to the end portion of the output shaft 50 are brought into meshing engagement with each other through an idle gear, not shown. By such rotation transmitting means, the output shaft 50 is rotated in a direction opposite to the direction of rotation of the pair of output side discs 4, 4 with the rotation of these output side discs 4, 4. Between the first half portion 15a and the other (left as viewed in FIG. 11) input side disc 2, the pressing device 9 of the loading cam type is provided as in the toroidal type continuously variable transmissions shown in FIGS. 5 to 7. A thrust ball bearing 88 is provided between the cam plate 10 constituting this pressing device 9 and a flange portion 17 formed on the outer peripheral surface of the front end portion of the second half portion 15b, whereby during the operation of the pressing device 9, the relative displacement of the cam plate 10 and the second half portion 15b in the direction of rotation is made free while a thrust load acting on the cam plate 10 is supported.
During the operation of the toroidal type continuously variable transmission shown in FIG. 11 which is constructed as described above, the pair of input side discs 2, 2 rotate at a time with the rotation of the input shaft 15, and these rotations are transmitted to the pair of output side discs 4, 4 at a time and at the same transmission gear ratio, and are transmitted to the output shaft 50 by the above-described rotation transmitting means and are taken out. At this time, the transmission of the rotational force is effected in two systems parallel to each other and therefore, great power (torque) becomes transmittable. Also, during the operation, the spacing between the pair of input side discs 2, 2 tends to be narrowed by the work of the pressing device 9. As the result, the inner sides 2a, 2a of the input side discs 2, 2 and the inner sides 4a, 4a of the output side discs 4, 4 strongly bear against the peripheral surfaces 8a, 8a of the power rollers 8, 8, whereby the transmission of power is effected efficiently.
In the case of the toroidal type continuously variable transmission of the so-called double cavity type as shown in FIG. 11 wherein the transmission of the rotational force is effected in two systems parallel to each other, it is necessary to make the angles of inclination of the trunnions 6, 6 installed in respective cavities, i.e., a first cavity 60 between one input side disc 2 and the output side disc 4 opposed to this input side disc 2, and a second cavity 61 between the other input side disc 2 and the output side disc 4 opposed to this input side disc 2, coincident with each other. If the angle of inclination of the trunnion 6 installed in the first cavity 60 and the angle of inclination of the trunnion installed in the second cavity 61 differ from each other, slip occurs on the portions of contact between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner sides 2a, 4a of the input side and output side discs 2 and 4, in the first and second cavities 60 and 61. Such slip not only aggravates the transmission efficiency of the toroidal type continuously variable transmission, but also becomes the cause of a trouble such as abnormal abrasion or burning in a remarkable case.
In contrast, in the case of a toroidal type continuously variable transmission of the known double cavity type, oil pressure fed into driving cylinders 31, 31 (FIG. 8) for driving trunnions 6, 6 installed in both cavities 60 and 61 axially of pivots 5, 5 has been controlled by a single control valve 37 (FIG. 10). Accordingly, the oil pressure bed into one driving cylinder 31 and the oil pressure bed into the other driving cylinder 31 become equal to each other. Also, not only the trunnions 6, 6 installed in the same cavity have been connected together by the cable 33 as shown in FIG. 6 and the angles of inclination of these trunnions 6, 6 have been made mechanically coincident with each other, but the trunnions 6, 6 in the different cavities 60, 61 have also been connected together by a cable and the angles of inclination of the trunnions 6, 6 in the both cavities 60, 61 have been made mechanically coincident with each other.
If forces required to displace the trunnions 6, 6 installed in the first and second cavities 60 and 61 axially by a predetermined amount are equal to each other, no problem will arise in particular even if the oil pressure fed into one driving cylinder 31 and the oil pressure fed into the other driving cylinder 31, regarding the both cavities 60, 61, are made equal to each other. However, when a toroidal type continuously variable transmission of the double cavity type is actually constructed, the amounts of displacement of trunnions 6, 6 installed in the cavities 60, 61 in the axial direction of the pivots 5, 5 (FIGS. 5, 6 and 8) differs from each other in some cases due to the difference in construction between the portions of the cavities 60, 61, or due to the difference in the amount of resilient deformation based on an unavoidable dimensional error in working even if the same forces are applied to these trunnions 6, 6.
Therefore, in the case of the toroidal type continuously variable transmission of the double cavity type according to the prior art, there cannot be denied the possibility that the transmission efficiency of the toroidal type continuously variable transmission is aggravated or a trouble such as abnormal abrasion or burning occurs, on the basis of the slip in the portions of contact between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner sides 2a, 4a of the input side and output side discs 2 and 4.